In order to inactivate viruses possibly contaminating plasma protein, such as albumin, an aqueous solution of the plasma protein has been heat treated (hereinafter referred to as the "liquid heating process") (Murray et al., The New York Academy of Medicine, 31, (5), 341-358 (1955)). The liquid heating process has been believed to be the most effective method for inactivating viruses. The effect of the process in the inactivation of viruses has been epidemiologically proved. Thus, this process has been commonly employed to date.
Among plasma proteins, however, only a few, including albumin, can withstand the above-mentioned liquid heating process. Those plasma proteins having a high physiological or biological activity are highly sensitive to heat and liable to be thermally denatured by this process. As a result, this process frequently can cause a decrease or loss of the activity of the plasma proteins.
Thrombin, which is a protein present in blood, is frequently accompanied by a risk of contamination with viruses, in particular, hepatitis or AIDS virus. Therefore, blood should be heat treated to thereby inactivate the viruses. However, thrombin per se is inactivated when it is heated in the form of an aqueous solution, i.e., in the above-mentioned liquid heating process.